As is well known, the heart has four chambers for receiving and pumping blood to various parts of the body. During normal operation of the heart, oxygen-poor blood returning from the body enters the right atrium. The right atrium fills with blood and eventually contracts to expel the blood through the tricuspid valve to the right ventricle. Contraction of the right ventricle ejects the blood in a pulse-like manner into the pulmonary artery and each lung. The oxygenated blood leaves the lungs through the pulmonary veins and fills the left atrium. The left atrium fills with blood and eventually contracts to expel the blood through the mitral valve to the left ventricle. Contraction of the left ventricle forces blood through the aorta to eventually deliver the oxygenated blood to the rest of the body.
Myocardial infarction (i.e., heart attack) can result in congestive heart failure. Congestive heart failure is a condition wherein the heart can not pump enough blood. When patients have a heart attack, part of the circulation to the heart wall muscle is lost usually do to a blood clot which dislodges from a larger artery and obstructs a coronary artery. If the clot is not dissolved within about 3 to 4 hours, the muscle which lost its blood supply necroses and subsequently becomes a scar. The scarred muscle is not contractile, therefore it does not contribute, to the pumping ability of the heart. In addition, the scarred muscle is elastic (i.e., floppy) which further reduces the efficiency of the heart because a portion of the force created by the remaining healthy muscle bulges out the scarred tissue (i.e., ventricular aneurism) instead of pumping the blood out of the heart.
Congestive heart failure is generally treated with lots of rest, a low-salt diet, and medications such as A.C.E. inhibitors, digitalis, vasodilators and diuretics. In some myocardial infarction instances, the scarred muscle is cut out of the heart and the remaining portions of the heart are sutured (i.e., aneurismechtomy). In limited circumstances a heart transplant may be performed.
Collagen-containing tissue is ubiquitous in the human body and makes up a substantial portion of the scar. Collagen demonstrates several unique characteristics not found in other tissues. Intermolecular cross links provide collagen-containing tissue with unique physical properties of high tensile strength and substantial elasticity. A property of collagen is shrinkage of collagen fibers when elevated in temperature. This molecular response to temperature elevation is believed to be the result of rupture of the collagen stabilizing cross links and immediate contraction of the collagen fibers to about one-third of their original linear dimension or the result of a change in the hydration of the tissue. Another property of collagen is that the caliber of the individual fibers increases greatly, over four fold, without changing the structural integrity of the connective tissue.
There has been discussion in the existing literature regarding alteration of collagen-containing tissue in different parts of the body. One known technique for effective use of this knowledge of the properties of collagen is through the use of infrared laser energy to effect tissue heating. The use of infrared laser energy as a corneal collagen shrinking tool of the eye has been described and relates to laser keratoplasty, as set forth in U.S. Pat. No. 4,976,709. The importance of controlling the localization, timing of laser energy delivery is recognized as paramount in providing the desired soft tissue shrinkage effects without creating excessive damage to the surrounding non-target tissues. Another known technique of altering collagen is described in U.S. Pat. No. 5,458,596 to treat joints. U.S. Pat. No. 5,437,664 describes using a catheter for venous occlusion and coagulation of blood.
Thermal destruction (i.e., ablation) of problematic myocardial tissue (i.e., arrhythmogenic focus) is a therapeutic procedure used with increasing frequency for the treatment of cardiac arrhythmias (e.g., ventricular tachycardia) as described in U.S. Pat. No. 5,246,438. The treatment of cardiac arrhythmias involves treating electrically problematic but otherwise healthy tissue. As a result one goal of ablation is to localize the heat as much as possible so as to restrict the ablation to only the problematic healthy tissue.